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Re: CO2 formula question
> From: Dennis8425 at aol_com
> Subject: CO2 formula question
> There are graphs to show relationship between GH, pH and CO2 concentration.
> But does anyone have an actual formula to do these calculations?
I posted it in March 1996, and the following posting was made in
> > From: "Loh Soon Hin" <lsh9933 at singnet_com.sg>
> > Subject: Re: KH,pH,CO2 table
> > > > pH as a function of CO2 concentration and KH value:
> > > > 7.58+@LOG(KH)-@LOG(CO2)
This was the one I posted in March 1996. The CO2 concentration
is in ppm.
> > > >
> > > > CO2 concentraction at a given pH and KH
> > > > 10^(7.58-pH+@LOG(KH))
> > What is the standard unit for KH?
> > A note under the Optimum CO2 Content Table in Dupla brochure says :
> > '' carbonate hardness in German degrees ( 1 degree dKH~ 10 ppm)''
> > However I had read from other references that say 1 German Degree equals
> > 17.9 ppm .
> This is a mess. One degree of _general_ hardness is defined as
> 10 ppm of calcium _oxide_ in the water. Of course, there is no calcium
> oxide actually in the water, but that is how it began, from a definition
> point of view. This corresponds to 17.9 ppm of calcium _carbonate_ in
> the water. (The molecular weight of CaO is 56, and that of CaCO3 is 100)
> There is no calcium carbonate in the water either.
> Now, if you dissolve either the oxide or the carbonate in water
> the reaction with CO2 will give you the bicarbonate. So, if you start
> from CaO, CaCO3 or even Ca(OH)2 and make a solution containing 1 degree
> of general hardness, you will end up with 1 degree of KH as well. The
> connection is solid, but almost Byzantine in its derivation! We are
> stating a bicarbonate concentration in terms of the equivalent amount
> (equal and opposite charge) of calcium, but stating that as either an
> oxide or carbonate amount.
> If we used millimolar concentrations of things, then this mess
> and a _lot_ of confusion would disappear.
> The equation relating pH, KH and CO2 concentration was originally
> posted by me on the APD in March. It was derived from the equilibrium
> for the reaction:
> "H2CO3" <-> H+ + HCO3-
> The tables on the Krib give somewhat different answers, which
> can be reproduced (at least as far as I have checked) by using the numbers
> 7.48 (for George's table) or 7.46 (for the Finnish one). The tables were
> derived using a different K for the reaction above. K _is_ temperature-
Paul Sears Ottawa, Canada